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The Case of the Virus That Stole Black Widow Spider DNA

Study finds bacteriophage contains genes coding for a toxin found in spider venom.

Wolbachia, a bacterium that specializes in infecting the cells of spiders and their relatives, has a viral infection. And the offending virus, called WO, appears to have stolen genes coding for a toxin found in black widow spider venom.

As one of the most common parasitic microbes in the world, Wolbachia has become a staple for many insects, and has evolved both parasitic and mutually beneficial interactions with its hosts.

Where there is Wolbachia, there is often the WO virus, which, like all bacterial viruses, aka bacteriophages, replicates itself inside of the bacterium.

But what is unique about WO is that it targets bacteria that live in the cells of animals, meaning this virus faces the usual bacteriophage challenge of having to exit and enter bacterial cells, along with the unusual challenge of first having to break out of, and then into, the surrounding animal cells.

How does this virus manage to overcome two sets of barriers, when other viruses only have to deal with one?

Reporting in the journal Nature Communications, Sarah and Seth Bordenstein of Vanderbilt University in Tennessee sequenced the genome of WO to find out.

Although the genome consisted of an unsurprising array of genes for infecting bacteria and self-replication, it also contained several genes that were highly similar to ones found in animal cells. One of these was the gene for latrotoxin — the toxin found in black widow spider venom.

“There hasn’t been another case of a latrotoxin being found outside of spiders,” Seth tells The Atlantic. In this case, the virus may use the toxin to burn holes through animal cell membranes, thus allowing the virus to escape from the cells.

Although many viruses are known to take genes from their hosts, they are normally limited to one particular group of hosts. Bacteriophages infect bacteria, and sometimes pick up their DNA. Viruses that infect animal cells can come away with small amounts of animal DNA. But this is the first reported case of a bacteria-targeting virus acquiring genes from an animal host.